Archive for February 7, 2014

Happy Birthday, Harry Nyquist!

Posted in History, The Universe and Stuff with tags , on February 7, 2014 by telescoper

Harry_NyquistThis morning I learned via Twitter that today is the 125th anniversary of the birth of Harry Nyquist, a physicist and electrical engineer, who was a prolific inventor who made fundamental theoretical and practical contributions to the field of telecommunications. He also gave his name to the Nyquist frequency and the Nyquist sampling theorem, now usually known as the Nyquist-Shannon sampling theorem.

Harry Nyquist (left) was born on February  7, 1889, in Nilsby, Sweden but moved to the United States in 1907. In 1917, after earning a Ph.D. in physics from Yale University, he joined the American Telephone and Telegraph Company (AT&T). There he remained until his retirement in 1954, working in the research department and then (from 1934) at Bell Laboratories.  Apparently he didn’t have a beard, but he seems to have overcome this obstacle and had an illustrious career in research.

In my opinion, Harry Nyquist’s achievements are not sufficiently appreciated either by physicists or by the wider world, so here’s a quick summary of some of his greatest hits:

Some of Nyquist’s best-known work was done in the 1920s and was inspired by telegraph communication problems of the time. Because of the elegance and generality of his writings, much of it continues to be cited and used. For example, his 1928 paper Certain Topics in Telegraph Transmission Theory refined his earlier results and established the principles of sampling continuous signals to convert them to digital signals. The Nyquist sampling theorem showed that the sampling rate must be at least twice the highest frequency present in the sample in order to reconstruct the original signal. These two papers by Nyquist, along with one by R.V.L. Hartley, are cited in the first paragraph of Claude Shannon’s classic essay The Mathematical Theory of Communication (1948), where their seminal role in the development of information theory is acknowledged.

In 1927 Nyquist provided a mathematical explanation of the unexpectedly strong thermal noise studied by J.B. Johnson. The understanding of noise is of critical importance for communications systems. Thermal noise is sometimes called Johnson noise or Nyquist noise because of their pioneering work in this field.

In 1932 Nyquist discovered how to determine when negative feedback amplifiers are stable. His criterion, generally called the Nyquist stability theorem, is of great practical importance. During World War II it helped control artillery employing electromechanical feedback systems.

I think that demonstrates the tremendous debt the modern world of telecommunications owes to Harry Nyquist, and why we should remember him on his 125th birthday..